1. Field of the Invention
The present invention relates to a technique for restoring an image forming apparatus from a power saving state.
2. Description of the Related Art
An image forming apparatus that can shift to a power saving state when print and scan functions are not being executed has been known. In the power saving state, power supply to a printer unit and a scanner unit (hereinafter, when appropriate, referred to for short as a printer unit and the like) for executing the functions is stopped. If the image forming apparatus is in the power saving state and a return factor is detected, power is supplied to the printer unit and the scanner unit. Examples of the return factor include pressing of a return button by a user.
Even if a return factor is detected, the printer unit and the like are not necessarily used. For example, when image data of a scanned document is stored into a memory of the image forming apparatus, power does not need to be supplied to the printer unit. In other words, if power is supplied to all the devices upon detecting a return factor, even unnecessary devices may be powered on.
A technique for performing control so that power is supplied to a device or devices that execute(s) the function to be used and not to a device or devices that execute(s) unused functions has been discussed in Japanese Patent Application Laid-Open No. 2002-359703.
An image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2002-359703 determines which device(s) to supply power to according to a factor for canceling a power saving state. More specifically, according to Japanese Patent Application Laid-Open No. 2002-359703, if a print request signal is received from an external apparatus, power is supplied to a printer unit to perform printing, and not to a scanner unit. If a sensor detects that a document is placed on the scanner unit, power is supplied to the scanner unit and not to the printer unit.
According to Japanese Patent Application Laid-Open No. 2002-359703 described above, no power is supplied to the printer unit and the like unless the printer unit and the like are determined to be used. More specifically, when a return button arranged on an operation unit is pressed, it is not yet determined whether to use the print and/or scan function(s). No power is thus supplied to the printer unit and the like. When the print and/or scan function(s) is/are subsequently determined to be used, power is supplied to the device(s) needed to perform the function(s) (see paragraph 0038 of Japanese Patent Application Laid-Open No. 2002-359703). In other words, according to Japanese Patent Application Laid-Open No. 2002-359703, no power is supplied to the printer unit and the like until the print and/or scan function(s) is/are determined to be used. The user therefore needs to wait until the power to the printer unit and/or the scanner unit stabilizes, while the printer unit and/or the scanner unit is/are reset, and while a preparation operation of the printer unit and/or the scanner unit (driving of the driving systems (motors)) is performed.
On the other hand, suppose that the preparation operation of the printer unit and the like is performed before it is determined whether to use the print and/or scan function(s). In such a case, the preparation operation can consume useless power unless the printer unit and the like are used. There is another disadvantage that the preparation operation of the devices produces noise if the printer unit and the like are not used.